Common hepatic duct

The common hepatic duct is a tubular structure in the biliary system that drains bile from the liver. It is formed by the union of the right and left hepatic ducts, which collect bile from the liver’s right and left lobes.^[5] The common hepatic duct is an essential conduit for bile flow, eventually merging with the cystic duct to form the common bile duct.

Location

The common hepatic duct is located in the upper right quadrant of the abdomen, beneath the liver.^[4] It runs parallel to the portal vein and hepatic artery in the hepatoduodenal ligament, forming part of the portal triad.

Anatomy

The common hepatic duct (CHD) is a vital component of the biliary system that transports bile from the liver to the common bile duct. Below is a detailed description of its anatomy:

Formation

• The common hepatic duct is formed by the union of the right hepatic duct and left hepatic duct, which collect bile from the liver’s right and left lobes.
• This confluence typically occurs near the porta hepatis, the gateway of the liver.

 Dimensions

• The CHD is approximately 4-6 cm in length and 4-6 mm in diameter in adults.
• Its size can vary depending on individual anatomy and conditions affecting the biliary system.

 Structure

• Lumen:
  • The inner lumen of the CHD is lined with simple columnar epithelium, which aids in bile transport and prevents backflow.
• Wall Layers:
  • Mucosa: Inner layer with smooth epithelium.
  • Submucosa: Contains connective tissue, blood vessels, and lymphatics.
  • Muscularis: A thin layer of smooth muscle fibers that facilitates bile flow.^[3]
  • Adventitia/Serosa: The outer connective tissue layer providing structural support.

Orientation and Location

• Course:
  • The CHD descends obliquely within the hepatoduodenal ligament, a peritoneal fold that contains the portal triad (portal vein, hepatic artery, and bile duct).
  • It is located anterior to the portal vein and to the right of the hepatic artery.
• Relation to Surrounding Structures:
  • Anterior: The peritoneum and the liver’s visceral surface.
  • Posterior: The portal vein.
  • Right: The cystic duct and gallbladder.
  • Left: The hepatic artery.

Junction with the Cystic Duct

• The common hepatic duct merges with the cystic duct from the gallbladder to form the common bile duct (CBD).
• This junction typically occurs near the lower edge of the hepatoduodenal ligament.

 Vascular Supply

• Arterial Supply:
  • The CHD is primarily supplied by branches of the right hepatic artery and occasionally the cystic artery.
• Venous Drainage:
  • Venous blood from the CHD drains into the portal vein.

 Lymphatic Drainage

• Lymphatic vessels from the CHD drain into the hepatic lymph nodes, which are located along the bile duct and near the portal vein.

 Nervous Supply

• Innervated by autonomic nerves:
  • Sympathetic Nerves: Derived from the celiac plexus.
  • Parasympathetic Nerves: Supplied by the vagus nerve.

Function

The common hepatic duct (CHD) is a crucial part of the biliary system that facilitates the transport of bile from the liver to the digestive tract. Its primary function revolves around bile conduction, storage regulation, and the coordination of bile flow to aid in digestion.

Here are some of its functions:

Transport of Bile from the Liver

• The CHD serves as a major conduit for bile produced by hepatocytes in the liver.
  • Bile is secreted into bile canaliculi, which merge into the intrahepatic bile ducts.
  • These ducts converge into the right and left hepatic ducts, which join to form the common hepatic duct.^[6]
• The CHD ensures the smooth and continuous flow of bile out of the liver.

Direction of Bile Flow

• Toward the Gallbladder:
  • When the digestive system is at rest (e.g., during fasting), bile flows through the CHD into the cystic duct and is stored in the gallbladder.^[2]
• Toward the Duodenum:
  • During digestion, particularly after a meal, bile flows from the CHD into the common bile duct and is delivered to the duodenum via the ampulla of Vater.

Regulation of Bile Storage and Release

The CHD collaborates with the cystic duct and common bile duct to regulate bile storage in the gallbladder and release into the small intestine.

• When the sphincter of Oddi (at the duodenum) is closed, bile is diverted from the CHD into the cystic duct and stored in the gallbladder.
• During digestion, the hormone cholecystokinin (CCK) triggers gallbladder contraction, and bile flows from the gallbladder through the CHD into the digestive tract.

Role in Fat Digestion

Bile transported by the CHD plays a key role in breaking down dietary fats:

• Bile salts emulsify fats into smaller droplets, increasing their surface area for enzymatic action by pancreatic lipase.
• This process is essential for the digestion and absorption of lipids and fat-soluble vitamins (A, D, E, and K).

Maintenance of Biliary Flow and Pressure

The CHD helps maintain a balance of bile flow and pressure within the biliary system:

• It allows bile to be stored in the gallbladder during periods of fasting, preventing excessive buildup of bile in the liver.^[2]
• During active digestion, it ensures that bile reaches the duodenum in a timely manner to aid in nutrient breakdown.

 Pathway for Waste Excretion

The CHD facilitates the excretion of waste products from the liver:

• Bilirubin: A byproduct of hemoglobin breakdown, which gives bile its characteristic yellow-green color.
• Cholesterol and Toxins: Excess cholesterol and fat-soluble toxins are excreted through bile transported by the CHD.

Coordination with the Pancreatic Duct

At the ampulla of Vater, the CHD typically merges with the pancreatic duct, ensuring the simultaneous delivery of bile and pancreatic enzymes to the duodenum.^[7] This coordination optimizes the digestive process by providing both bile and enzymes to break down macronutrients.

Clinical Significance

The common hepatic duct (CHD) is essential for bile transport, and its dysfunction can lead to significant clinical conditions:

• Biliary Obstruction: Blockage of the CHD by gallstones, tumors, or strictures can cause obstructive jaundice, dark urine, pale stools, and pruritus due to bile buildup.
• Cholangitis: Infection of the bile ducts, often resulting from obstruction in the CHD, leads to fever, abdominal pain, and jaundice (Charcot’s triad).^[8]
• Bile Duct Injury: Accidental injury to the CHD during surgeries like cholecystectomy can lead to bile leakage and require reconstructive procedures.
• Tumors: Cholangiocarcinoma (bile duct cancer) can develop in or around the CHD, causing progressive bile duct obstruction and severe jaundice.
• Mirizzi Syndrome: A rare condition where gallstones compress the CHD externally, causing symptoms of biliary obstruction.